Almost all monkeys live in troops of several females with young and either a single male (as in hamadryas baboons, mandrills, most guenons and langurs) or several (as in marmosets, tamarins and vervet monkeys). Like other primates, they are largely social animals that have a menstrual cycle, although unlike chimpanzees and humans, their sexual activity is generally more limited in extent and duration.
Most species are diurnal, active during the day. Monkeys are very flexible and adaptable, living in a variety of habitats from rainforest to desert to mountains. They are omnivorous and feed on nuts, seeds, fruits, leaves, flowers, bark, roots, vegetables, insects, rodents and birds.
Scientists classify Old World and New World monkeys into six families: Cercopithecidae, Callitrichidae, Cebidae, Aotidae, Pitheciidae and Atelidae. New World monkeys, also known as neotropical or neotropical primates, are distinguished from their Old World counterparts by their prehensile tails, which they use to grasp branches when moving through the trees. They also lack the bare pads on their rumps that their Old World cousins have.
Monkeys use a variety of vocalizations including barks, screams, grunts, squeaks, hoots and wails to communicate with each other. They can also use facial expressions to convey mood and threat, such as a raised eyebrow indicating “stay away–I’m in a bad mood.”
Some monkeys have thick fur to help them survive harsh environments. For example, some Japanese macaques, called snow monkeys, bathe in hot springs during the winter to keep warm.